Preheat oven to 160C/320F and line an 8 inch/20cm square pan with baking paper. Grease well with butter or non stick cooking spray.
Melt butter then add sugar, cocoa and salt. Allow to cool a bit if really hot. Then add rum and eggs. Finally fold in flour and chocolate chips.
Now spread half them mixture into your prepared pan. Dollop spoonfuls of dulce de leche evenly across the batter. Top with the remaining batter making sure the dulce de leche is covered.
Bake for 35 to 45 minutes. Really, I guess you should allow then to cool completely but a brownie is really at it's best gooey and warm even if it doesn't cut so cleanly.
If you should leave out the dulce de leche only bake your brownie for 20 to 25 minutes